Electron discharge device



Se t. 5, 1950 w. G. SHEPHERD ELECTRON DISCHARGE DEVICE Filed June 28, 1946 WI/EN TOR I44 6. SHE PHE R0 BY A 7 TORNE 1 manning FIG.

'IIIIIIIIIIIII' Patented Sept. 5, 1950 ELECTRON DISCHARGE DEVICE William G. Shepherd, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 28, 1946, Serial No. 679,967

Claims.

This invention relates to electron discharge devices and more particularly to microwave oscillators of the reflex type.

In one known general construction, a reflex oscillator comprises an enclosing vessel housing a cavity resonator having a gap therein, an electron gun for projecting an electron stream across the gap in one direction and a repeller electrode for causing reversal of the direction of the electron stream after it has crossed the gap and again projecting it into the gap. In their first traversal of the gap, the electrons are velocity varied due to the field within the resonator and when they are reinjected into the gap they constitute a density varied stream and. deliver energy to the field noted thereby to generate and sustain oscillations. For given electrode potentials, the oscillation frequency is determined largely by the constants of the resonator.

In some applications, it is desirable that the oscillation frequency be variable over a fairly wide range and to be accurately adjustable to any desired frequency in this range conveniently. Such frequency adjustment may be effected by alteration of the configuration of the cavity resonator, for example by displacement of a flexible wall portion thereof. In devices intended for operation at extremely high frequencies, specifically frequencies corresponding to wavelengths of the order of 5 centimeters or less, necessarily the resonator dimensions must be small. Hence, even slight changes in a dimension of the resonator may cause a large variation in the resonant frequency thereof.

In accordance with one feature of this lnvention, the cavity resonator, the tuning mechanism therefor and the enclosing vessel of the device are constructed and arranged so that physical changes in the tuning mechanism and the enclosing vessel with variations in tempera ture have substantially no effect upon the characteristics of the cavity resonator, whereby frequency drift with temperature variations is minimized.

More specifically, in accordance with one fea ture of this invention, the cavity resonator is provided with a disc-like flexible Wall to which a tuning lever is coupled and the lever is constructed and' arranged so that its direction of major thermal expansion and contraction is substantially normal to the direction in which the wall is displaced by flexure'to tune the resonator.

In accordance with another feature of this invention, the resonator and the support or fulcrum of the lever are mounted on the enclosing electron discharge device illustrative of one em--' bodiment of this invention; I Fig. 2 is an exploded perspective view showing details of the'tuning mechanism for the cavity resonator, included in the device illustrated in Fig.1;and

Fig. 3 is a view in section and partly diagrammatic of a portion of an electron discharge device illustrative of another embodiment of this invention.

Referring now to the drawing, the device therein illustrated comprises a highly evacuated metallic enclosing vessel including a base portion or member ID and a flanged cup-shaped portion ll seated upon the base member ID and joined hermetically thereto as by welding or brazing the portion ll having a wall HA parallel to the base portion. Ill. Seated ona recess in the base member ID is a mounting or saddle member I2 upon which a unitary electrode and resonator assembly is supported.

This unitary assembly comprises a toroidal metallic cavity resonator, designated l3 as a whole, secured to the mounting or saddle member l2 and having a corrugated flexible metallic wall I 4 and an exterior annular flange 15. The

resonator includes also an inwardly extending, stepped cylindrical member IE to the inner end of which a centrally apertured, dished grid II is affixed. Opposite and .in alignment with the grid I1 is a second, centrally apertured dished grid I8, which is supported by the corrugated wall M.

A cylindrical insert I9 is secured within the member 16 and constitutes the end electrode of an electron gun.

The electron gun comprises a cathode memher at which i's'mounted on an insulating plate 2| and is provided with a circular, concavoconvex end portion 22, the concave face of which is coated with a thermionic material. The cathode member 29 is'provided in one wall with a suitable aperture through which a heater element 23 is inserted. Encompassing the cathode member is a beam-forming electrode which is-v cathode are concentrated'into a converging beam focussed uponthe gapbetween the grids I1 and The insulating plate 2| may be seated upon the base member ID and fixed in position by .a

pair of braces or struts 25, only one of which is shown in the drawing.

Secured to the flange l5 on the resonator is" a ring 26 which is provided with *a-plurality of fingers 21 and mounts a second insulating. plate 28. The plate 28, in turn, mounts a dished repeller electrode 29, opposite and axially aligned with the grids and I8 and having locking tabs"30 which extendithrough slots in: the 'plate 5 centrally apertured spider :member 3 isxprovided with fingers 32 each of whichis secured .to'a re spective finger 21 of-"the mounting ring -26, and v 28 and arebentovenagainst thisFpl'atez has locked inthe central aperture therein 'a pro tuberance -33 on' adished disc '34.

as by welding, to' a: respective finger 36 *of an annulus 37, the fingers 36 extending through oversize aperturesinthe insulating iplate'28i The annulus 31' is dished as illustrated; and has its central portion secured"to:'the-flexible wa1l'|4 of-the cavity resonator;-

The disc '34"andannulus-3'| ,'because of their form; arerelativelymigida' The spider member 3| constitutes a flexible coupling between the?- ring 26; which is fixed in positionrand the unit composed of the disc34 and'annulusr3l sothat motion of the unit mentioned results-"in fie'xureof the wall I4 and, hence, in alteration of'ithe" resonant frequency ot thecavity' resonator. Con

trolled motion'isimparted to' the *unit'by way of a lever arm 38 'which has one-endmortion fitted'on the protuberance--33 and is-pivotedupon and hermetically, sealed" to: a laminated metallic diaphragm-39in turn sealed hermetically'to the:

cup-shaped portion |A-of the 'enclosing vesselr The lever 38 is subject to'actuation by a differential 'screw" arrangement" whereby accurateadjustment of its position andj hencejaccurate" tuning of the cavity resonator-mayberealized:

Specifically, the outerend'of' the lever extends into and is fixed to' a nut member 40- slidable" upona seat 4| 'seated"upon the'diaphragm"30f the member '4B being "provided withatr'apped portion for accommodating the 'tuningscrew 42."

The tuning screw is supportedupon'a frame- 43 secured to a support 44 in turn aifixed to the portion HA of the enclosing'vessel,"and is provided with a head 45 for facilitatingmanipula tion thereof .and'a stop.nut for limiting displacement thereof in one direction As shown clearly. in Fig. 1, an enlarged-portion oflthe tuning screw is threaded into a tappedinsert 41 fixed on the-frame 43 by one or more set screws 48,-whichmay be utilized also to lockthe tuning screw in any desired'position'. In order to eliminate back lash a helical spring 49 -may be :provided in engagement with the frame 43 and nut member 40; Also'a bowed thrust spring 50 extending through a slot in the nut member 40 *andhaving its ends locked in slots in the frame 43 maybe provided'to'maintain a substantially constant contact force between the nut member 40 and the tuning screw.

As is apparent, rotation of the tuning screw 42 results in displacement of the nut member 40 and consequent rocking of the lever 38. Rocking of the latter is translated into displacement of the flexible wall l4 to tune the cavity resonato'r." It will 'be notedzathat the direction of displacement of the flexible wall portion I4 is at substantially right angles to the length of the lever 38 so that expansion and contraction of the-lever with temperature variations has substantially no effect upon the flexible wall portion M and, consequently, substantially complete thermal segregation, in effect, is attained between the tuner mechanism and the cavity resonator wherebydrift in the resonant frequency of the resonator with variations in ambient temperature is minimized. Moreover, it will be noted that substantial segregation thermally, in so far as the effect of'expansio'n and contraction of' the portion H of the enclosing vessel upon: the resonant frequency of the resonator is concerned;

is realized dueto-the-fact that the direction in which the major dimensional variation with temperature of theportionl occurs is at right angles to the direction of displacement of the flexible portion |4 requisite'tocause'a change Such expansion and contraction of .ithevessel H); H,"

| lA as may occur in the direction'pa'rallerto the in the tuning of thecavit'y resonator.

base portion H] 'has littleefiect upon the tun' ing cavity because; for such conditions-the ful=-'- crum point for the lever "and the support point for the resonator will be displaced in" the same direction and to substantially:equal extentswith,

therefore, substantially no change "in the' rel'a'-- tive location of I these points1 Thus, not only is accurate tuning-of the res-- onator enabledbut yariationin the resonant frequency with temperature changes is "substantially.-

minimized;

The base Ill has secured theretoan insulat ing plate 5| which carries terminal prongs52 'to which leading-in conductors-53 are connected These conductors extend through eyelets 54in the base IO 'and are sealed hermetically to theeyelets by vitreous beads 55. Connection'between that may be employed. The-de'side'ratumof both' high frequency operation and stable operation may be achieved by coupling an external cavity resonator of high Q to the cavity resonator l3. Such an external resonator is indicated in broken outline at 51 in Fig. 1. The coupling is efiected by a conductor 58 which has an-inner end'loop portion 59 and is sealed in a vitreous head 60 inturnsealed toan eyelet 6| -afiixed tothe base ID. Because of the mannerof'mountingthe resonator |3, i.

thecoupling conductor 58 may be made very short, of the order of one-half 'wavelengthof the operating frequency of 'the device, whereby -'a' close'andefficient coupling of the external rese., upon the'base l0 and with its, axis parallel thereto, it will benoted 'that" onator or guide 51 to the internal resonator I3 is realized.

In the operation of the device, electrons emanating from the coated cathode portion 22 are concentrated into a converging beam focussed upon the gap between the grids I? and i8 and pass through the central openings in the grids H and i8. In crossing the gap, the direct current beam is converted into a velocity varied beam. The latter enters the region between the grid I8 and repeller electrode 29 and because of the low potential upon the latter electrode the direction of electron motion is reversed and the electrons are again projected into the gap in the form of a density varied beam and deliver energy to the field within the resonator whereby oscillations are sustained. The grids and the repeller electrode are so constructed and arranged, for example in accordance with the principles set forth in Patent 2,411,913 of December 3, 1946 of John R. Pierce and William G. Shepherd, that the reversed electrons enter the gap in the form of a diverging beam and after crossing the gap are collected by the member l6, whereby, as pointed out in the application noted, electronic hysteresis effects are minimized.

It will be noted that in crossing the gap in the forward direction, the electrons pass through the central apertures in the grids ii and i8 and, hence, cross the gap at a region where the field is relatively weak. In crossing the gap in the reverse direction, however, the electrons pass through the grid [3 and, thus, traverse regions where the field is relatively strong. Thus, the modulation coefficients for the two directions of electron motion across the gap are diiierent, that for the reversed electron stream being greater than that for the forwardly moving stream. This construction is favorable to the realization of high operating efiiciencies.

Different modulation coefficient for the two directions of electron motion across the gap in the cavity resonator may be realized advantageously also in the construction illustrated in Fig. 3. As shown in this figure, the cylindrical member 18 is provided with an inwardly extending cylindrical portion 65 across the inner end of which an electron permeable member such as a grid I19 extends. The electron trajectories are illustrated by the broken lines E. It will be noted that in their forward motion, that is from left to right in Fig. 3, the electrons in crossing th gap between the electron permeable members or grids ill and M30 traverse a gap of length greater than the length traversed in the reverse direction, i. e., from the grid 60 to the electron receiving member 66, which is the dished end 66 upon the member l6. Consequently, a weaker modulation coefiicient exists for the forward transit of the electrons across the gap than for the reverse transit.

The resonator in the device illustrated in Fig. 3 may be tuned in the same manner as that in the device shown in Fig. 1 and described heretofore. In order to simplify the drawing, the tuning mechanism has been omitted from Fig. 3.

Although specific embodiments of thi invention have been shown and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

Reference is made of Patent 2,466,062, issued April 15, 1949 to William D. Stratton wherein a related invention i disclosed.

What is claimed is:

1. An electron discharge device comprising an enclosing vessel having a pair of opposed wall portions, a cavity resonator mounted upon one of said wall portions and having a wall displaceable in the direction substantially parallel to said one wall portion, and a tuning lever coupled to said displaceable wall, mounted from the other of said wall portions and extending substantially normal to said direction.

2. An electron discharge device comprising an enclosing vessel having a pair of substantially parallel wall portions, a cavity resonator mounted by one of said wall portions and having a wall flexible in the direction parallel to said one wall portion, and a tuning lever fulcrumed upon the other of said wall portions, connected to said flexible wall and extending substantially normal to said parallel wall portions.

3. An electron discharge device comprising a metallic enclosing vessel having a base and a wall portion opposite said base, a cavity resonator mounted upon said base and having a flexible disc wall portion substantially normal to said base, a flexible member mounted on said wall portion of said vessel, and a tuning lever mounted on said flexible member, extending substantially parallel to said flexible disc wall and connected to said flexible Wall.

4. An electron discharge device comprising a metallic enclosing vessel having a base and a wall opposite said base and substantially parallel thereto, a substantially toroidal cavity resonator affixed to said base and having its axis substantially parallel thereto, said resonator having a wall portion movable in the direction parallel to said base, a flexible member afiixed to said wall, and a tuning lever fulcrumed on said flexible member, extending substantially normal to said axis and connected to said movable Wall portion.

5. In combination, an enclosing vessel having a flexible wall portion, a cavity resonator within said vessel and having a flexible wall, and means for tuning said resonator comprising a lever fulcrumed on said wall portion, extending substantially parallel to said flexible wall and having one end connected thereto.

WILLIAM G. SHEPHERD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,506 Hahn June 2'7, 1944 2,304,186 Litton Dec. 8, 1942 2,309,966 Litton Feb. 2, 1943 2,396,802 Mouromtsefi et al. Mar. 19, 1946 2,402,119 Beggs June 18, 1946 

